Kurt Suzuki's two-run double in the 10th inning lifted the Washington Nationals to a 6-4 win over the St. Louis Cardinals in the second of three games from Busch Stadium.
Washington still holds a four-game lead over Atlanta for the top spot in the National League East, as the Braves won on Saturday. Either a win or Atlanta loss over the final four games will clinch the first division crown for the Nationals since the team moved to the nation's capital.
"These games definitely get you ready," Suzuki said referring to the playoffs. "Those guys are scrappy, they're a good team."
Also, Washington leads Cincinnati by one game for the best record in the majors as the Reds lost to the Pirates on Saturday.
Michael Morse hit a grand slam in the first inning for the Nationals, who have won three of their last four.
Jordan Zimmermann gave up three runs on seven hits with two walks and five strikeouts over 6 1/3 innings for Washington. Drew Storen (3-1) got the win despite allowing St. Louis to tie the game in the ninth inning.
Peter Kozma went 3-for-4 with two RBI and two runs scored while Jon Jay drove in two for the Cardinals, who had won five of six coming into the game. Kyle Lohse gave up the grand slam and eight hits overall with nine strikeouts in six innings.
St. Louis' lead over the Los Angeles Dodgers for the final wild card spot in the National League has slipped to two games as the Dodgers downed Colorado on Saturday.
"We came back from a four-run deficit, that's a pretty good spark," Cardinals manager Mike Matheny said. "The team didn't roll over. That's not the issue. We got close, but didn't finish it off."
With Sam Freeman (0-2) on the mound for St. Louis in the 10th, Adam LaRoche walked on four pitches to start the inning and moved to second on a Roger Bernadina sacrifice bunt. Ian Desmond then flied out and Danny Espinosa was issued a free pass. A passed ball moved each runner up a base and Suzuki scored them both with a double to left-center.
Craig Stammen allowed Matt Holliday to lead off the bottom of the inning with a single, but got Allen Craig to hit into a 6-4-3 double play and struck out Yadier Molina for his first career save.
With one out in the first, Bryce Harper singled for Washington, Ryan Zimmerman doubled and LaRoche walked to load the bases.
Morse then lined a shot that hit the top of the wall in right that appeared to be a home run. First base umpire Chris Guccione did not rule it as such, though.
Harper scored and Morse rounded first base before trying to get back to first. St. Louis second baseman Skip Schumaker took a throw from Carlos Beltran and tagged out Morse.
The umpires then went to review the play and after returning, ruled it a home run. They made Harper, who sat in the dugout during the review, take third base and had the other runners return to their bags. The umpires had Morse return to home and he mimicked a swing to re-enact the grand slam and then touched all the bases.
The game stayed that way until the seventh, when the Cardinals got back in it. With one out, Beltran singled and Schumaker followed suit. Kozma then ripped a double to score two and after David Freese walked, Zimmermann's night was done.
Sean Burnett then took the mound for Washington and was greeted by a Jay single that made it a 4-3 game. Burnett then got Matt Carpenter to fly out and Ryan Mattheus retired Holliday to end the frame.
Tyler Clippard walked the Cardinals' Yadier Molina with one out in the eighth, but then got Beltran to hit into a 6-4-3 double play to end the frame.
St. Louis, though, tied the game in the ninth off Storen, as back-to-back one- out singles from Kozma and Daniel Descalso put runners at the corners before Jay's sac fly to center tied the contest.
Washington has won four of the six games against St. Louis this season ... Washington left 10 men on base while St. Louis stranded seven ... Morse has two grand slams this season and four for his career.